The stages were dismantled, the microphones muted. This was not a day for squabbling voices among Egypt's growing band of protesters. Instead, the plan was for Tahrir Square to reverberate with a single, simple demand. Military rule must end, and end now, the crowd roared as one. The time for compromise was over.

But compromise is exactly what the ruling generals had in mind as they unveiled the new prime minister, Kamal el-Ganzouri, the latest weapon in their battle to shut down a crisis that has now claimed more than 40 lives and thrown the country's political landscape into turmoil. A former Mubarak-era prime minister, Ganzouri, 78, is reprising his old position at a time when the public appetite for genuine change has never been fiercer.

The supreme council of the armed forces [Scaf] will be hoping he can convince the wider public that their transition plan – including national elections that, improbably, are due to start in just two days time – remains credible.

In central Cairo, 100,000 people felt very differently.

"I'm not ideological and I don't care about politics, but you don't have to be political to know that when rulers decide to kill their own people, their time is up and they have to leave," said Ahmed Kandil, a 23-year-old business consultant who joined the anti-Scaf rally. "What I've realised this week is that right now thousands and thousands of people are speaking out against these massacres, and collectively we are roaring." And so Egypt is in deadlock once again, torn between an authoritarian regime in the palace and a grassroots uprising at the gates – with a political class stumbling around the middle ground trying to capitalise on piecemeal concessions from above.

Ten months on from the toppling of Mubarak, as military helicopters whirred above Tahrir and marches swept in demonstrators from all directions, a sense of deja vu permeated the square.

The difference was that, as of Friday night, the new targets of the revolution remained unmoved from their thrones, despite international opinion now turning notably against them. In its strongest statement yet on the continuing unrest, the White House called on the generals to immediately cede power to Ganzouri's civilian government, which is expected to be formed in the next few days. It marked a notable shift in policy from the US administration, which funds the Egyptian military to the tune of $1.3bn (£842m)a year and up until now had backed Scaf's intention to maintain a major political role for the next 18 months or more.

Seven straight days of deadly violence can quickly reshape political realities, and Washington is not the only place where support for Scaf appears to be rapidly deteriorating. In the early afternoon, two officers appeared on a balcony overlooking Tahrir Square and led chants against Field Marshal Mohamed Hussein Tantawi, Scaf's leader and their own commander-in-chief. They joined a small but expanding group of mid-ranking officers who have effectively defected in recent days and allied themselves with the protesters.

"I want the people to know there are army officers who are with them," Major Tamer Samir Badr told the Guardian. "My feelings came to a head last week when I saw people dying, and the army gave the orders for us to just stand and watch. I'm supposed to die for these people, not them die for me. Now I'm ready to die in the square, and I'm not afraid of anything."

Speaking next to an open window that looked out on to Tahrir and which Badr insisted was left open so that he could hear the crowds, the 37-year-old claimed that many other officers had been attending the protests secretly in civilian clothes. "Scaf is composed of 19 generals and they are the ones who have power in this country. But those 19 are nothing compared to the thousands of people in the forces. I demand that the field marshal hand over power to a civilian government immediately, and that he just leave," he said.

"Of course this puts me in danger, but I am on the right side. I'm with the people. If I die, I will die with a clean conscience. Either I will get killed in the square, or get sent to a military court then prison."

If the desertion of some of their juniors has spooked Egypt's generals, they are being careful not to show it.

Ganzouri's appointment was widely interpreted as a calculated snub to the protesters occupying central Cairo and other major squares around the country, replacing one uninspiring Mubarak-era politician with another. While Mohamed ElBaradei – the more radical alternative who many protesters would like to see heading a new civilian government – prayed with demonstrators in Tahrir, Ganzouri gave his first press conference and said in a somewhat faltering manner that he was no puppet of the armed forces which appointed him.

"The powers given to me exceed any similar mandates," he declared, looking uncomfortable and frequently pausing for long periods as he spoke. "I will take full authority so I'm able to serve my country."

The speech prompted derision in the square, where crowds chanted "illegitimate" and dispatched some of their number to begin a sit-in at the nearby cabinet office. "Everything about this f*****g 'transition' is old and expired: Scaf, their prime minister, and their teargas," posted Egyptian journalist Sarah Carr on Twitter.

As the day wore on clashes between police and demonstrators were reported in the Nile delta town of Mahalla el-Kubra as well as the upper Egyptian city of Minya and several other smaller locations. In the capital, three human chains of protesters stopped anyone from approaching a 10ft concrete barricade put in place by soldiers to separate armed police and revolutionaries on Mohamed Mahmoud Street, where most of this week's deaths have taken place.

Two large banners strung across the road renamed the thoroughfare as Street of the Martyrs and Eyes of Freedom Street, the latter a reference to the dozens of protesters who are believed to have been blinded by what appeared to be the deliberate firing of birdshot by security forces at head height.

Despite the relative calm on Friday, nearby field hospitals continued to tend to patients. "This protest is more important than 25 January [the start of the anti-Mubarak uprising]," argued Mohamed Nabeel Elmasry, one of several volunteers who helped protect the medical facilities from being swamped by the crowds. "I live in New Jersey and haven't been back to Egypt for 20 years, but I came today because we had promises from the military council and those promises were broken. We're a trusting people and we gave them a chance, even though they felt like an extension of the old regime. And then through action after action after action, they showed us we were wrong."

What the generals' next action will be remains to be seen, as does the outcome of the parliamentary vote, which is scheduled to start on Monday.

It seems remarkable that Egyptians will begin queuing at polling stations even as multiple parties withdraw from the race, city centres remain occupied by protesters and bloodshed continues on the streets.

But then nothing in this country has been unremarkable over the past 10 months and, judging by the current atmosphere in Cairo's Tahrir Square, it seems that is the way things are set to stay.